The evils of exchanging scions

Axel(12b/Sunset H2)May 9, 2012

Well, here it is, after an unusually cool Spring, I got to discover how some of the scions I've obtained through exchanges have apple mosaic virus and have infected some of my trees. What surprised me is that the virus showed up from various different sources, which makes me wonder how prevalent infected wood is.

So far, only GRIN wood and Maple Valley orchard wood has proven to be virus free. Fedco trees, CRFG exchanges and Botner all appear to be sources of infected wood. CRFG is by far the worst offender, which makes me seriously question if I would consider grafting wood from CRFG exchanges without knowing where it came from.

It's really worth paying a little extra to get clean wood.

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Konrad___far_north(3..just outside of Edmonton)

Yes, one never knows for sure when getting untested scion or when trading.

I know, your knife is out allot,...I found out, the more you graft onto one tree the more it is prone the get infected.

    Bookmark   May 10, 2012 at 12:40AM
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sonny44

Ugh, this really puts a damper on my plans for next spring.
How can you tell if scions are infected?
Is there anyway you can treat/soak the wood before grafting to kill the virus?

    Bookmark   May 10, 2012 at 6:55AM
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Scott F Smith(6B/7A MD)

Ouch. I have a tree with Botner wood that has been looking fine for several years but this year it looks like it has AMV, the first time I have seen it in my orchard. Is it common for it to take several years to appear? The tree was transplanted this year so maybe the shock had something to do with it. Or maybe its not AMV. I am more familiar with the fig version of mosaic, it often does not express itself but tends to come out when trees are under stress.

For those with a lot of varieties, an advantage of the close hedgerow plantings as opposed to the n-way graft is you can check the spread of these diseases - nearly all of the spread is through trees with more than one variety on them.

Scott

    Bookmark   May 10, 2012 at 8:26AM
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fruitnut Z7 4500ft SW TX

I've got some type of virus in most of my multigrafted plums and pluot. It causes bleaching of the leaf margins after mid season. Can't say it really hurts the tree or fruit but it's still a warning. So I'm taking Scott's approach and going to smaller single-variety trees at closer spacing mostly on dwarf roots.

    Bookmark   May 10, 2012 at 10:15AM
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Axel(12b/Sunset H2)

The closer spacing will help a little but isn't full proof because the roots between trees will naturally graft to each other below ground. Essentially, once the virus is in your orchard, there is a likelihood it will show up elsewhere.

Scott, the apple virus is the same, it expresses itself under stress. On many varieties, it never even shows, the only way to know if the wood is infected is by grafting an indicator variety to it. Granny Smith and golden delicious are two varieties that are highly susceptible and will show symptoms.

My approach is to use kelp spray mixed with serenade to boost the immune system of the apple trees. The kelp provides required micro-nutrients and the Bacillus subtilis in serenade is also known to stimulate the natural immune response of plants. It won't get rid of the virus, but the plants are less affected.

The virus removal process is straight forward but time consuming. Here is the process:

  • Year 1) Graft infected wood onto a potted rootstock

  • Year 2) Place growing tree into controlled heated environment to keep the tree at a constant 38C temperature for 8 days.

  • Year 2 + 1 or 2 months) take fresh budwood and graft onto virus free rootstock. (In the professional procedure, the fresh budwood is collected right after the heat treatment and then grown in-vitro via micro-culture. The reason is that fresh growth is usually virus free. So the combined heat treatment plus immediate fresh growth collection ensures a high rate of success of virus removal.)

  • Year 3) Let graft grow out and observe to make sure the virus was successfully inactivated by grafting indicator variety.

If the virus was not successfully inactivated, repeat procedure. This procedure is worth it if you have an old unique heirloom and you want to make it available to everyone.

Now, keep in mind, most people who do exchange scions have Franken-trees. This does significantly increase the chances of virus infected wood to circulate. There is the possibility to heat treat wood before you graft it but it would work only on summer budwood, Winter wood would start to bud out and no longer be graftable. Of course, there is the possibility of collecting and heat treating the wood right after a late Fall leaf drop. Since the wood has not yet been chilled, it would not bud out at that time.

Note: heating your in-ground tree to 38C for two weeks won't work. The roots also have the virus. However, if you have super-dwarf trees, you can dig them up and go though this procedure on the tree itself.

One more note on viruses. I did have an interesting discussion with the fellow who runs Tress of Antiquity. He tells me that people did remove the viruses out of cox orange pippin, but the resulting wood after the in-vitro procedure resulted in a cox orange pippin that produced inferior tasting apples. So either the in vitro process caused a mutation, or the viruses actually contribute to improved flavor in the fruit. So virus...

    Bookmark   May 10, 2012 at 1:21PM
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Scott F Smith(6B/7A MD)

Axel, thanks for the information. I am probably just going to pull up this particular tree and hope that wipes out that patch at least. It has Sam Young and Newtown Spiztenberg on it from Botner. Below are some pics, let me know what you think having seen more. It could be chemical or related to all the unusual cool weather we had, I'm not completely sure. Oddly enough also one of my peaches has mottled leaves. It doesn't look like any viruses I have seen but I think I am going to remove it just for good measure.

Scott

    Bookmark   May 10, 2012 at 7:46PM
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marc5(6aOH)

Oh no.....two years ago I ordered budwood for several apple varieties from Botner. The budded trees are now growing in my orchard! So far they are healthy.

What is the probability that my trees have the virus? Do orchardists ever destroy their trees just on the outside chance that they are infected? That would be really sad.

Marc

    Bookmark   May 10, 2012 at 10:55PM
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Axel(12b/Sunset H2)

Scott, that is the tell tale of apple mosaic virus. It's more likely to show symptoms if the Spring weather is cool. I am not removing my trees, because there really is no point. I have no way of knowing which varieties are truly infected, because symptoms are often not visible. The only way I would know for sure is if I only grafted from virus free sources. Unfortunately, this isn't possible.

Speaking of scion wood exchange, i got a pigeonnet rouge from you a couple of years ago, and it's got leaves that are red when they emerge, and they slowly turn dark green, more akin of a red fleshed apple. However, the pigeonnet rouge from Geneva does not have red leaves. Anything red fleshed growing close to your pigeonnet rouge that could have been sent to me by mistake?

    Bookmark   May 10, 2012 at 11:24PM
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Scott F Smith(6B/7A MD)

Axel, that wood is almost certainly Belle Fleur Rouge if it came from my orchard, its my only red-leafed apple. Its a huge apple with a taste in the McIntosh school. Its also a seriously lanky tip-bearer so watch how you prune it. The tree isn't near Pigeonnet Rouge but I expect the "Rouge" names got crossed at some point. If you have "BFR" from me and its not reddish then that is probably the real Pigeonnet Rouge.

Scott

    Bookmark   May 10, 2012 at 11:38PM
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ramble

Is this phenomenon a real threat to J Plums or Cherries gratfing? Or mainly apples?

    Bookmark   May 11, 2012 at 3:27PM
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Scott F Smith(6B/7A MD)

All fruit trees have viruses so its a problem everywhere. On stone fruits there are 3-4 viruses that are fairly common. But, they don't seem to be as common as the apple viruses. The really bad one on stone fruits, plum pox, has not yet established itself in this country (it did try a couple of times). If that one shows up the stone fruit virus problem will quickly surpass the apple virus problem.

Scott

    Bookmark   May 11, 2012 at 4:53PM
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Axel(12b/Sunset H2)

Add to that the fact that the apple mosaic virus affects both apples and stone fruits. It's the same virus in both plant families.

All grafting runs the risk of introducing viruses, especially when people do multi-varietal grafts. So for example you could have a nice virus free lapins cherry, and do a couple of grafts of some older varieties that might have viruses. Then you decide to exchange scion wood of your lapins cherry. Et voila, now an infected lapins cherry is in the scion exchange flow.

Bottom line is that grafting often leads to virus infections, the only way is to stick with known virus free sources.

    Bookmark   May 12, 2012 at 1:18PM
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BaaBaaRaa(5)

OhOh..... I am heading to the CRFG's scion exchange tomorrow, and was basically looking for suggestions for scions to graft to my apple and pear trees.

I got scion wood there 2 years ago. It was my first time grafting to established trees. The only graft that actually worked (and produced a misshapen apple) was Mutsu. I was discouraged (some of the grafts grew but later died), so I skipped last year. I am attaching a photo of my only success so far, 2 year old Mutsu graft's only fruit. (Grafted to a Granny Smith)

Now I want to try again. I guess I will just take my chances and hope for the best. Thanks for the info though. I never would have thought that. I am going to the one at Cabrillo Hort in Aptos CA.

    Bookmark   January 12, 2013 at 5:43PM
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marc5(6aOH)

I'm reviving this thread because it looks like my fears were realized. Is this apple mosaic virus? It's on my Ashmead's Kernel, scionwood from Botner. Out of a handful of scions from him, this is the only one--so far--exhibiting the signs. Bummer--I really was excited about this variety. The tree has been in my orchard one year, and it's 6' tall.

Would you burn it now and cut your losses? Apparently I can expect 0 to 50 percent yield reductions from this virus, and possible infection of my other trees, is this right? My trees are on 20'x20' spacing. If I destroy this tree, is there any chance that a replacement planted in the same spot might contract the virus?

Any suggestions for virus-free Ashmead's Kernel? Mine is on G30 from Cummins.

Thanks,
Marc

    Bookmark   May 27, 2013 at 11:35PM
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canadianplant

This is vaguely reminding me of the spread of chestnut blight in the early 20th century.......

I was going to start to multi graft my trees, but got a bit paranoid as to where I get the scion. We dont have too many problems up here due to the winter (for the most part) but my neighbor, who has been growing fruit for 70 years (here for 50) has noticed ore problems in the last 15 years in regards to disease and pests.

The only place I would aquire scion, is from a very cold place, which is not prone to virus. Even then, I would have to assume that isnt even fool proof.

Axel - You make a great point many people seem to forget about the root grafting, but it does depend on the tree. I belieive cherry roots try their hardest to stay away from other cherry roots, while apples dont seem to mind at all.

There is also the pest problem. Suckering insect spread the virus too. You can have a clean orchard, and still have a group of say, aphids come in, and spread the disease from miles away. We cannot get rid of all pests all the time, and we cannot stop the trees from grafting together. On top of that, add close proximity planting, and the disease will just follow the line down the orchard.

The only way around it, is to stop spreading the diseases through scion swaps, but, what gardener doesnt want to share their trees?

    Bookmark   May 28, 2013 at 8:17AM
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Scott F Smith(6B/7A MD)

Marc, what I did was destroy the tree and replant in the winter, giving 6 months for the soil to sit. Maybe that was not long enough. With your large spacing I would just replant a bit off on the spacing in a fresh spot, it won't be noticeable when the trees are large that one is a few feet off.

Scott

    Bookmark   May 28, 2013 at 1:00PM
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alan haigh

Folks have been exchanging scions for centuries. I do nothing but manage fruit trees and a big part of what I manage was planted before plant viruses were known. I myself have been actively grafting wood from these trees for about 15 years and managing most of the trees I've grafted- hundreds of them.

In all this time I've never experienced a noticeable virus problem, so I really don't think people should get excessively alarmed. If you have viruses that you don't know about and you get less yield than you would from virus free stock- so what? I believe viruses are more a problem for commercial growers who must get the highest yields possible to stay in business.

If you are just starting an orchard and have access to most of the varieties you want to grow virus-free, I can see going that route for sure, but if I had done this when I started, I doubt I'd be getting more pleasure or even much more yield from the trees I have in my own orchard. There are so many other more important challenges between a home orchardist and the crop, in my opinion.

Not that this isn't an interesting topic for discussion, or that it isn't a good idea to note particularly virulent sources of wood but I don't want people excessively concerned about the threat- we have enough to worry about.

    Bookmark   May 28, 2013 at 3:23PM
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Axel(12b/Sunset H2)

I wouldn't take such a lax perspective. The USDA has been hard at work in eradicating viruses out of apple stock in the US. Botner and CRFG exchanges are the only places I've gotten viruses from. It's to the point that I think I may start to keep a small batch of granny smiths around just to use as testing material before I let the material in my orchard. At this point, I have at least 5 trees I have to remove, some are pretty big.

The apple mosaic virus can be killed with heat. The scion wood essentially gets flash pasteurized and the buds get grafted afterwards. Apple mosaic is dormant and symptom fee in some species and shows up especially with multi-grafts.

    Bookmark   May 28, 2013 at 4:13PM
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Axel(12b/Sunset H2)

I wouldn't take such a lax perspective. The USDA has been hard at work in eradicating viruses out of apple stock in the US. Botner and CRFG exchanges are the only places I've gotten viruses from. It's to the point that I think I may start to keep a small batch of granny smiths around just to use as testing material before I let the material in my orchard. At this point, I have at least 5 trees I have to remove, some are pretty big.

The apple mosaic virus can be killed with heat. The scion wood essentially gets flash pasteurized and the buds get grafted afterwards. Apple mosaic is dormant and symptom fee in some species and shows up especially with multi-grafts.

    Bookmark   May 28, 2013 at 4:18PM
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alan haigh

Axel, the USDA may be working hard at eradicating viruses from commercial stock but the concern may have little to do with the concerns of non-commercial growers. The viruses are out there and pretty much beyond eradication when apple trees sprout up in so many different places and beyond the sphere of the USDA.

The reason you are concerned is because it has been a problem for you- maybe because you have so many varieties in so little space from so many different sources.

If and when it becomes a problem for me in even one of the scores of orchards I manage, I too will become concerned, but if the problem was as severe as you portray it I don't see how I've avoided it so far with such a wide range of sites where I'm planting new trees next to 100 year+ apple trees multiple times every season. In addition to this I'm often hired as a consultant on sites where I've been sought because of difficult problems others were unable to diagnose.

I admit it could possibly be a problem that I'm overlooking where production is less than I'd like but I am unaware of the cause- not every orchard I manage does as well as I would like. Still, I haven't seen any obvious symptoms.

Many of my sites have old trees nearby that aren't going to be removed unless they die so viruses are pretty much a fact of life here. We still get plenty of fine apples. Maybe in the climate here the viruses are less destructive.

    Bookmark   May 28, 2013 at 5:01PM
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marc5(6aOH)

Hman, are you saying that you have seen no symptoms of virus in your orchards, or that you have seen the symptoms on leaves but the yield loss is insignificant?

Marc

    Bookmark   May 29, 2013 at 11:13PM
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alan haigh

I've never diagnosed virus problems in any of the orchards I manage. I don't believe symptoms are always visually apparent.

There are so many challenges managing fruit in the northeast, I focus on the obvious ones and that keeps me busy and worried enough.

    Bookmark   May 30, 2013 at 4:53AM
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canadianplant

Doesnt that completely ignore the fact that "Resistant" trees dont show symptoms, yet still spread it? The only way to know is if you get the plants tested or expose it to a non resistant type....

    Bookmark   May 30, 2013 at 8:38AM
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